@le_data contains the lines of the file (which is a total waste of memory, incidentally). @line contains the fields. You never use contents of @line.

Also, your indexes make no sense. The fields are indexed 0 to 4, but you're accessing index 6.

use strict;
use warnings;

my $width = 11;

my $le = "lethal_results.txt";
open(LE , "<", $le)
   or die("Unable to open file $le: $!\n");

while (<LE>) {
   chomp;
   my @line = split(/\s+/, $_);
   if ($line[4] >= 50) {
      printf("%s%${width}s%${width}s%\t\t%.6g\n",
         @line[0,1,2,4]
      );
   }
}
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